What are the possible diagnoses tests?
A blood test is usually required to diagnose malaria, although the blood can be used in a number of different ways. The most common, traditional form of diagnosis is a blood smear, observed under a microscope by a qualified technician. These can be “thick” or “thin”; the “thick” smear examines a whole drop of blood for the presence of the malaria parasites infecting the patient’s red blood cells. Because a relatively large volume of blood is examined in this way, the thick smear is useful for detecting low levels of parasites in the blood, and therefore is good for an initial “positive or negative” diagnosis. The thin smear allows for a closer look at the infected blood cells, and thus can be used to identify the species of malaria, which can be important for giving the patient appropriate treatment. The danger with blood smears is that very low intensity infections can sometimes be missed, given the a low number of parasites in the blood.
More recently, a number of antibody tests have been developed to test for malaria. These so-called “rapid diagnostic tests” (or RDTs) do not require the expertise of a blood smear and only need a tiny droplet of blood, and so can even be performed at home as part of a self-testing kit. Different tests have been developed to test between the various different species of malaria. While quick and easy, there are some concerns over the sensitivity and specificity of the various tests; trials in the field have gone some way to quantifying the effectiveness of these tests in different contexts. One potential advantage of RDTs is that in some cases they seem capable of positively diagnosing low intensity infections, that would be missed by traditional blood smear. A disadvantage for wide-spread use of these tests, especially in low resource settings, is that they are very expensive.
Finally, the advent of DNA-based techniques for identifying malaria parasites means that PCR (polymerase chain reaction) can be used on a patient’s blood for an almost fool-proof diagnosis, not only of species but also, to a certain extent, of intensity. However, this procedure takes time, is expensive and requires a fully equipped laboratory with trained personnel; as such, it is not usually used for every day diagnosis of malaria infections, and especially not in developing countries where the vast majority of malaria cases occur.